Manufacture of pulp and paper



Patented Feb. 21, 1933 UNITED STATES LINN BRADLEY, OF MONTGLAIR, NEW JERSEY,

PATENT OFFICE- AND EDWARD P. MCKEEFE, OF NEW YORK, N. Y., ASSIGNORS TO BRADLEY-MCKEEFE CORPORATION, OF NEW YORK, N. Y.,

A CORIiORATION OF NEW YORK MANUFACTURED]? PULP AND PAPER 1T0 Drawing.

This invention relates to improvements in the manufacture of pulp and paper from wood, and includes improvements in the method of production of the pulp and paper, as well as in the pulp and paper themselves. The invention is of particular value for the production of pulp and paper from hard woods which are ordinarily considered of little or no value for the production of pulp and paper; and the improved process of the invention enables high grade pulp and paper to be produced therefrom.

In the improved method of the present invention the wood is subjected to a chemical cooking or pulp making operation with a sulfite cooking liquorcontaining sulfur dioxide or sulfurous acid combined with a suitable base e. g. soda; and with an amount of sulfur dioxide or sulfurous acid radical in excess of that required for the formation of the normal sulfite (Na SO but 'less than that re-.

quired for the so-called acid sulfite, e. g., sodium acid sulfite (NaHSO The common methods of producing wood pulp chemically are the so-called soda, sulfate and sulfite processes. In the so-called soda process, the main cooking operation is dependent upon caustic soda, and the process is limited in its commercial application to a few woods, notably poplar. In the so-called sulfate process, the main cooking operation is dependent upon caustic soda assisted more or less by sodium sulfide, although some sodium carbonate and sodium sulfate may be present; and the commercial application of the sulfate process is similarly limited to a few so-called pulp woods. In the so-called sulfite process, the main cooking operation is carried out with a bi-sulfite solution in the presence of an excess of sulfurous acid.

calcium bi-sulfite with excess sulfurous acid forming the preponderating amount of cooking liquor commercially used. The sulfite processissimilarlv limited in its commercial application to a few woods such as spruce, balsam and fir. In the soda and sulfate processes. so-called, the cooking liquor is strongly alkaline, while in the sulfite process the cooking liquor is strongly acid; and it has been considered impractical to cook wood are ordinariliy Application filed September 27, 1923. Serial No. 665,224.

successfully for the production of a chemical pulp unless the cooking liquor was either strongly acid or strongly alkaline.

In our prior application, Serial No. 481,147,

filed June 28, 1921, we have set forth an im-- I proved process for the manufacture of chemical pulp in which the wood is subjected to a cooking operation with a cooking liquor containing essentially a normal alkali sulfite; and we have found that such method presents many important advantages from a commercial standpoint in the manufacture of chemical pulp from Wood, and especially hardwoods (deciduous trees having short fibres).

Asa result of our further investigations we have found that a greatly improved result can be obtained, as compared with the ordinary sulfite process, by carrying out the cooking operation with a liquor containing sodium sulfite and containing an amount of sulfurous acid less than that required for sodium bisulfite. Such a cooking liquor is therefore intermediate in character between a cooking liquor'containing only normal sodium sulfite (Na SU5) and one containing only sodium bisulfite (NaHSU e havefound that a cooking operation carried out with such a cooking liquor differs in important respects from that,of the ordinary sulfite process. We have found, for example, that up to a certain point, and even though a considerable amount of sulfur dioxide or sulfurous acid radical is present, over and above that required to form normal sodium sulfite, the cooking liquor nevertheless is alkaline to litmus, and, where there is used a suflicient amount of the chemicals in the cooking liquor, the residual liquor is similarly alkaline to litmus. y

We havefurth'er observed that, with such a regulated sulfur dioxide or sulfurous acid radical "content, the cooking operation takes place without the necessity of relieving sulfur dioxide from the digester, as in the ordinary sulfite process.

e have moreover found that woods which considered of little or no value for the pro notion of high grade pulpby the ordinary sulfite process, can be satisfactorily cooked by the process of the present invention and give a high grade pulp. In particular, we have found that hard woods, for example woods such as birches, beeches and maples, which are not ordinarily considered as pulp Woods, will give a high yield of excellent pulp, when treated by the process of the present invention. The invention accordingly makes possible the production of high grade pulp from Woods not ordinarily considered as pulp woods, thus accordingly greatly extending the available supply of woods from which high grade pulp can be produced.

We have found not only that such dense hard woods can be satisfactorily cooked for the production of chemical pulp, but we have found that such woods present advantages in the way of large yields per cord and high grade of pulp obtainable therefrom which make them of particular value as pulp woods, when treated according to the present invention. The invention, however, is not limited in its application to the treatment of such dense hard woods, for it is applicable to the treatment of woods commonly considered as pulp woods, as well as woods which are not commonly considered aspulp woods. The rapidly decreasing supply and the increased cost of the common pulp' woods makes the invention of particular importance because it makes commercially available Woods which are not ordinarily considered as pulp woods.

The invention moreover presents important advantages for treating dense hard woods and it is of particular importance and value as applied to the treatment of such woods and the production of pulp therefrom. The pulp produced from such dense hard woods by the present invention is of distinctive character and is quite different in its properties from the pulps commonly produced commercially by the so-called sulfite process.

In the common sulfite process the cooking liquor is strongly acid with free sulfurous acid in excess of that required for the formation of the bisulfite,'and such an acid cooking liquor tends to injure the fibres of the wood and to give a harsh pulp. The process of the present invention avoids the production of such a harsh pulp and gives a distinctive and superior pulp, even from the a regulated amount of excess sulfurous acid or sulfite' radical, above that corresponding to normal sodium sulfite, accordingly appears to have an important and advantageous action which differs somewhat from that obtained with normal sulfite alone in the cooking liquor; while the action is also distinguished from that which takes place with a strongly acid cooking operation such as that of the ordinary sulfite process.

Where the amount of excess sulfurous acid or sulfite radical (beyond that corresponding to normal sodium sulfite) is small, and up to the point where a considerable excess is present, the cooking liquor is alkaline to litmus. The amount of excess sulfurous acid or sulfite radical may be as high as about 25% of the total sulfurous acid or sulfite radical present in the cooking liquor. With a suffici'ently large excess, the cookingv liquor becomes acid to litmus. For example, with around 80% excess, the cooking liquor was found to be slightly acid to litmus. An excess of 25% to 30% forms an advantageous cooking liquor for cooking dense hard woods, i. e. 25% to 30% of the total sulfurous acid or sulfite radical present being in excess of tfzihat corresponding to the normal sodium sul- Using the present invention with dense hard woods, 9. digester charge of wood chips contains a considerably increased weight of wood as compared with the weight of wood in the charge of the same digester in the ordinary sulfite process; and with increased weight of wood tobe cooked, an increased amount of chemical is required for the cooking operation; but it is an important advantage of the present invention that a sufiiciently strong cooking liquor can be readily prepared and used for-cooking such dense hard woods without objectionable injury to the fibres, with the result that an increased yield of pulp can be obtained per digester charge. I

The residual liquor produced by the processof the present invention is also of a distinctive character, presenting important differences and distinctions from the ordinary waste sulfite liquor so called. In particular it contains a higher percentage of base than does the Waste liquor from the ordinary sulfite process, while both the nature and the amount of the constituents present appear to be quite different in character.

The invention will .be further illustrated by the following specific example but it will be understood that the invention is illustrated thereby and is not limited thereto.

made up of sodium sulfite with an excess of sulfurous acid or sulfite radical over and above that corresponding to the normal sodium sulfite, this excess being for example 30%, so that of a totalof 700 lbs. of sulfur dioxide, about 490 lbs. would represent that required to form normal sodium sulfite, and about 210 lbs. would be in excess of that amount. The digester can be charged with the chips and cooking liquor inthe usual way, as in other pulp processes. The digester can be heated by direct steam, care being taken to circulate the liquor to give all the chips a substantially uniform treatment, and with relieving of air and other gases as may be found necessary during the progress of the cook. The heating with steam can for example be carried out so that a steam gauge pressure of 140 lbs. is reached in about one to two hours from the time the steam is turned on, and the cooking operation can then be continued at approximately such pressure (i. e. at a temperature corresponding to saturated steam at a pressure-of about 140 lbs. gauge pressure) for from three to four hours or until the cooking operation is completed; after which the digester can be discharged into a blow-pit in the .usual way. The pulp can then be drained to separate the residual liquor and then Washed and subsequently treated in the same way as chemical pulp produced by other processes. Dense hard woods of the character mentioned give a light colored pulp of superior properties, being made up of fine needle-like fibres and being well .adapted for use either directly or after further treatment in the manufacture of paper or for admixture with other pulps such as mechanical or ground wood pulp for the production of news print or. similar papers.

The amount of sodium sulfite as Well as the amount of excess sulfurous acid or' sulfite radical, can be varied, and, in general, where less of the cooking reagents are used, a somewhat longer time is required for the completion of the cooking operation. With dense hard woods, for example, the cooking liquor I may contain a high percentage of the sulfurous acid or sulfite radical in the form of normal sodium sulfite or corresponding thereto, and a relatively low excess of the sulfurous acid or sulfite radical, (in excess of the amount corresponding to normal sodium sulfite.) Considering the 'total sulfurous acid or sulfite radical in this way (i. e. considering the total sulfite radical as combined to form normal sodium sulfite, to the extent of the sodium present and the remainder in excess of that amount), the excess of sulfurous acid or sulfite radical may vary from a small percentage up to around 40% or even more of the total sulfurous acid or sulfite radical present. We refer to the excess sulfurous acid or sulfite radical in this way merely for convenience of expression, for it may be possible that both normal sodium sulfite and sodium bisulfite are present in thecooking liquor as well as the sulfite of sulfurous acid radical, and possibly complex combinations.

It is one advantage of the present invention that a fairly high concentration of chemicals in the cooking liquor can be used without objectionable injury to the fibres of the pulp, inasmuch as the cooking liquor is free from the strongly acid character of the ordinary sulfite cooking liquor. The wood can accordingly be readily cooked with less danger of the pulp being-injured or over cooked. Moreover, with the improved process of the present invention the chemical reaction of the cooking liquor upon the Wood appears to be of a different and distinctive character, the excess sulfurous acid or sulfite radical apparently first acting upon the wood and bringing about a preliminary disintegration with reduction in the excess uncombined sulphur dioxide content of the liquor. A large amount of what may be considered as combined sulfite is nevertheless present and similarly appears to have an important action in carrying the cooking operation to completion and in preventing objectionable injury to v the fibres.

The invention is applicable not only to dense hard woods but it is also applicable to ordinary pulp woods such as spruce and poplar. With poplar, for example, using a cooking liquor' containing about 30% of the total sulfurous acid or sulfite radical, as excess sulfurous cid or sulfite (calculated as give a light colored stock of a very free running character, and with high yield, the residual liquor drawn off from the pulp being greenish in color. With such a cooking liquor, even though slightly acid to litmus, and although cooked in an iron digester, the chips and pulp gave no apparent indication of contamination by iron.

As compared with the cooking of wood with normal sulfite of sodium, without .excess sulfurous acid-,or sulfite radical, the present invention presents the advantage that less sodium is required. in the cooking operation, and less sodium is present in the residual liquor, so that a correspondingly less amount of the sodium is required to be recovered or otherwise obtained in the further carrying out of the process. Where, for example,

fite radical (as hereinbefore Calculated), the.

um sulfite without excess sulfurous acid or sulfite radical. \Vith the excess sulfurous acid or sulfite radical, the process also partakes of a different nature, as already explainedr On the other hand, the invention is distinguished from acid sulfite processes such as commonly used commercially, in which an excess of free sulfurous acid is used in excess of that corresponding to the acid sulfite or bisulfite, and the present invention presents many advantages overf such processes, as already mentioned.

While with the ordinary calcium bisulfite cooking liquors, an excess of free sulfurous acid is necessary, to hold the calcium bisulfite in solution and to give a sufficient strength of cooking liquor, it is possible with the present invention to obtain a sufficient strength and concentration with a less amount of sulfurous acid or sulfite radical than that corresponding to the bisulfite.

The residual liquors produced by the processes of the present invention can be used to a greater or less extent in the carrying out of further cooking operations, with suitable additions thereto, such as additions of sulfur dioxide, or of sulfur dioxide and sodium sul fite, to make up the cooking liquor to the requisite strength. Instead of using the residual liquor without treatment, it may be subjected to various methods of treatment for the recovery'of sodium sulfite, or a mixture of sodium sulfite and sodium bisulfite there from. The residual liquor can thus be concentrated and calcined and the calcined product leached and treated with sulfur dioxide; while some of the sulfur dioxide given off during the calcination can be recovered and utilized. The sodium sulfite or acid sulfite thus recovered or regenerated can be supple mented by the addition of such further amounts of sulfite or bisulfite or of sulfur dioxide as may be required in the making up of the cooking liquor for further use in the carrying out of the process. In determining the excess of sulfurous acid or sulfite radical we have found it convenient to utilize standard alkaline titration methods, titrating first With phenolphthalein as an indicator and standard caustic soda solution to determine the. excess sulfurous acid or sulfite radical and then with methyl orange as an indicator and with standard sulfuric acid to determine one-half the'total sodium content, and calculating the relation of the excess to the total sulfurous acid or sulfite radical from the figures so obtained.

Instead of using a sodium sulfite cooking liquor of regulated excess sulfurous acid or sulfite radical, the sodium may be to a greater or less extent replaced by magnesium, so that the cooking liquor contains both sodium and dioxide until a sufficient excess of free sulfurous acid is present, and then treating the resulting solution or mixture with sodium sulfate, which, in the presence of such excess acid, will react with the calcium sulfite 0r bisulfite to form calcium sulfate which will be precipitated as gypsum and sodium sulfite or bisulfite which will remain in solution in admixture with the magnesium sulfite or bisulfite. The resulting solution of sodium and magnesium sulfites can then be further modified if necessary to give it the desired content of excess sulfurous acid or sulfite radical, and the solution adjusted to proper strength can then be used as a cooking liquor in the carrying out of the process of the invention. We do not limit ourselves however to any particular method of producing the cooking liquor as it is evident that any suitable method may be employed. Q

The sodium content of the cooking liquor can be replaced to a greater or less extent by potash; that is,a potassium sulfite'cooking liquor, or a cooking liquor containing both potassium and sodium sulfites, together with a regulated excess of sulfurousacidor sulfite radical, can be used instead of the sodium sulfite cooking liquor. These are to be considered so far the equivalents of sodium as to fall within the scope of the following claims. For example, where salt deposits containing both sodium and potassium salts. are available and are utilized in making the cooking liquor, both potassium and sodium sulfites may be present in the cooking liquor;

although the commercial availability of sowood to a cooking operation under pressure and at an elevated temperature with a sodium sulfite cooking liquor containing an amount of sulfurous acid or sulfite radical greater than that corresponding to normal sodium sulfiteand less than that corresponding to sodium bisulfite, at leastabout 25% but less than 40% of the total sulfurous acid or sulfite radical being in excess of thatcorresponding to the normal sodium sulfite, and the amounts of the sulfites of sodium being sufficient sothat substantially all of the acid radicals present in the resulting residual liquor are in the form of salts of sodium.

3. Themethod of'preparing paper pulp from wood which comprises digesting particles of wood :with a solution containin magnesium bisulphite, an alkali sulphite and an alkali bisulphite. I

4. The method of preparing paper pulp from wood which comprises digesting particles of wood with a solution containing magnesium bisulphite, sodium sulphite and sodium bisulphite.

5. The method of preparing paper pulp from resinous woods which comprises digesting particles of resinous wood with a solution containing magnesium bisulphite, sodium sulphite and sodium bisulphite, in the substantial absence of calcium compounds.

6. The method of preparing paper pulp from woods which comprises digesting particles'of wood with a solution containing magnesium bisulphite, an alkali bisulphite and S0 ions over and above those resultmg from the dissociation of the magnesium and alkali bisulphites.

7. The method of preparing paper pulp from Woods which, comprises di esting particles of wood with a solution containing magnesium bisulphite, sodium bisulphite and 0 ions over and above those resulting from the dissociation of the magnesium and sodium bisulphites.

8. The method of preparing paper pulp from woods which comprises digesting particles of wood with a solution containing magnesium bisulphite, an alkali sulphite and an alkali bisulphite in the substantial absence of calcium compounds.

9. The method of producing pulp which comprises subjecting wood to a cooking operation in a liquor containing sodium bisulfite and sodium monosulfite in such proportions and amounts based on the wood cooked that sodium monosulfite will be present throughout the cooking operation.

10. The method of producing wood pulp which comprises subjecting wood to a cooking operation in a liquor containing sodium bisulfite and sodium-monosulfite, the total sO content of such liquor being not less than about one-fourth of the dry weight of the wood and the amount of sodium monosulfite being sufficient so that substantially all acid radicals present in the residual liquor at the termination of the cooking operation are present as salts of sodium. 11. The method of producing Wood pulp which comprises subjecting wood to a cooking operation in a liquor containing sodium bisulfite and sodium monosulfite, the ratio of sodium to S0 and the amounts thereof being adaptedto retain substantially all of the S0 in a salt or salts ofsodium throughout the cooking operation.

12. The method of producing wood pulp which comprises subjecting wood to a cooking operation in a liquor containing sodium bisulfite and sodium monosulfite, less than 40% of the total S0 content of the liquor being'in excess of that required to form monosulfite, the amounts-of these two compounds of sodium being sufficient so that the resulting residual liquor at the termination of the cooking operationcontains substantially all of its acid radicals in the form of salts of sodium.

13. The method of producing wood pulp which comprises subjecting wood to'a cooking operation in a liquor containing sodium bisulfite and sodium monosulfite, at least about 25% but not substantially more than 30% of the total S0 content of the liquor being in exce'ss'of that required to form monosulfite, and the amounts of monosulfite and bisulfite beingsufficient so that sodium monosulfite is present throughout the cooking operation. 7

14. The method of producing wood pulp which comprises subjecting wood'to a cooking operation in a liquor containing sodium bisulfite and sodium monosulfite about 30% of the total SO content of the liquor being in excess of that required to form. monosulfite, and the amounts of sodium bisulfite and of sodium monosulfite being sufficient so that sodium monosulfite is present in the residual liquor-at the end of the cooking operation.

15. The method of producing wood pulp which-comprises subjecting wood to a cook ing operation in a liquor containing sodium bisulfite and sodium" monosulfite the amount of monosulfite based on the weight ofgthe wood being sufficient to maintain the liquor substantially non-acid to litmus throughout the cooking operation and continuing the cooking operation until the fibres have been rendered readily separable from each other. 16. The method of producing pulp, which comprises subjecting wood to a digesting operation at elevated temperatures and under pressure by means of cooking liquor containing sodium bisulfite and sodium monosulfite in amounts and proportions based on the wood cooked so that the amount of sodium 10 sulfite is sufiicient to react with all of the organic acids formed from the Wood during the digesting treatment so that the residual liquor at the termination of the cooking operation contains all of such organic acids in the form of a salt or salts of sodium and so that substantially all of the sulfur dioxide 1 contained in the cooking liquor is present in the said residual liquor in the form of a salt or salts of sodium.

17. The method of producing pulp, which comprises subjecting wood to a digesting treatment at elevated temperature and under pressure by means of cooking liquor containing sodium bisulfite and sodium monosulfite in amounts and proportions based on the Weight of the Wood so that there is present in the cooking liquor throughout the digesting treatment an amount of sodium monosulfite that is sufiicient to combine with the acids present in the liquor or formed therein to such an extent that the residual liquor at the termination of the digestingtreatment is sub stantially non-acid to litmus. l

a 18. The method of producing chemical I pulp from wood, which comprises digesting the Wood in a digester under pressure and at an elevated temperature with a cooking liquor containing both sodium monosulfite and sodium bisulfite, less than 40% of the total S0 content of the cooking liquorbeing in excess of that required to form sodium monosulfite with all of the sodium content of the said monosulfite and bisulfite, these sulfites beingsupplied to the cooking liquorin amounts sufficient to retain therein substantially all of the S0 and the organic acid radicals derived from the Wood in the form of salts of sodium, the digesting treatment being carried out at temperatures up to at least about 17 0 degrees centigrade, and the digesting treatment being continued until a suflicient amount of the non-fibrous content of the wood has been rendered soluble in the liquor to render the fibres readily separable from each other by blowing the fibrous material and residual liquor from the digester under steam pressure of about 80 pounds per square inch.

-In testimony whereof we aflix our signa- 60 tures.- i

LINN BRADLEYI EDWARD Pl MoKEEFE. 

